The invention pertains to a metal-cutting tool comprising a disk-shaped or blade-shaped basic body with at least one recess for receiving a cutting insert with lower, upper and rear contact surface, which [insert] is interchangeably clamped securely in the recess by an elastically spreadable clamping arm forming the upper contact surface of the recess, while the mutual contact surfaces of the cutting insert and the recess are designed to fit together positively.
The so-called xe2x80x9cself clamping principle,xe2x80x9d according to which the cutting insert is securely clamped in a recess in the basic body of the tool by a part of said basic body designed as an elastic clamping arm, is primarily applicable in the case of long, narrow cutting inserts, such as are used in tools for grooving or plugging, or also in side-milling cutters.
The clamping power that securely clamps the cutting insert in the receiver represents the elastic force of the clamping arm, which is either automatically spread apart to make clamping contact when the cutting insert is pushed into the receiver or spread beyond the clamping position with a suitable tool prior to the seating of the cutting insert, whereby the positioning of the cutting insert in the receiver is facilitated.
The maximal clamping force that can be applied is limited for constructive or technical material reasons, so that it is possible for the cutting insert to be dislodged from the receiver, especially in the case of side-milling cutters involving high centrifugal forces when in use, and also in the case of grooving tools when the tool is withdrawn from the groove or in boring operation.
It is therefore important in the case of these tools that adequate measures be taken to preclude the inadvertent dislodgment of the cutting inserts from the receiver.
DE OS 30 44 790 describes a side-milling cutter in which the cutting inserts are wedge-shaped and their clamping in the basic body of the tool is achieved by wedging in the similarly wedge-shaped receiver slit with one of its arms designed to be partly elastic.
Disadvantageous here is the fact that the cutting insert has no defined depth stop, so that the wedging can be either too tight, resulting in difficulty in loosening the cutting insert during change-over, or too loose, resulting in inadvertent loosening of the cutting insert due to centrifugal force when the tool is used.
Furthermore, exact mutual positioning of the individual cutting edges is only possible with difficulty.
EP 0 660 785 describes a metal-cutting tool of the general type cited in the preamble, especially a grooving tool, in which the cutting insert has several variably inclined partial surfaces on its contact surface facing the clamping arm, while the clamping arm engages two differently inclined partial surfaces in a defined manner, so that the cutting insert should not be readily dislodged from the clamped position even when subjected to tensile stresses.
Disadvantageous in the case of such a design is that the clamping force is applied primarily in the direction of the lower contact surface of the cutting insert and the component of the clamping force that presses the cutting insert against the rearward stop and therefore protects against a dislodgment of the cutting insert from the receiver very small, so that in many applications the cutting insert can still be pulled out of the receiver.
It is therefore the objective of the present invention to create a metal-cutting tool of the general type cited in the preamble, in which the cutting insert can be easily seated in the receiver recess, while at the same time a securely clamped position is ensured even against
This is accomplished according to the invention, in that the lower contact surface of the cutting insert is delimited by a convex arc with the radius (R) and that the lower contact surface of the recess is delimited by a concave arc with the radius (r), wherein R greater than r, whereby two defined contact points (A) are formed at approximately the beginning and the end of the contact surfaces, further that the upper contact surface of the cutting insert and the contact surface of the clamping arm are matched together in such a way that the charging of the contact surface with the clamping force occurs in an area which is at a distance from the symmetry line (S) in the direction of the cutting edge of the cutting insert, so that the symmetry line (S) is the normal on the connecting line (V) of the two contact points (A), which symmetry line, halves the separation of the two contact points (A).
By reason of the arc configuration of the lower contact surfaces according to the invention and the opposing eccentrically applied clamping force, the clamping force is applied at about 60% to the lower contact surfaces and about 40% to the rearward contact surfaces. The arc configuration of the lower contact surfaces can extend over the entire contact surface or over only the sections at the beginning and the end of the contact surface in the immediate vicinity of the complementary contact points (A). The difference of the radii of the two contact surfaces can be very slight and can be only a few tenths of a mm in actual practice.
Especially in conjunction with an inclination of the rearward contact surfaces in the direction of the active cutting edge of the cutting insert, so that they describe an acute angle (xcex1) with the connecting line (V) of the contact points (A), a good wedging of the cutting insert in the receiver is achieved and dislodgment of the cutting insert from the receiver by tensile or centrifugal forces is precluded.
According to the invention, for a better application of the clamping force in the correct area on the cutting insert, the recess for the cutting insert must be so configured that it has its narrowest slit width in the area according to the invention.
Due to the fact that the radius (r) of the arc of the lower contact surface of the recess is smaller than the radius (R) of the arc of the associated contact surface of the cutting insert, a precisely defined two-point contact is theoreticallyxe2x80x94when viewed from the sidexe2x80x94achieved. In actual practice and because of the slightly different radii of the contact surfaces as well as high surface pressures, linear or a real xe2x80x9ccontact pointsxe2x80x9d are realized, which, due to production tolerances or dimensional variations in the course of frequent change of the cutting insert, can shift slightly from the theoretical contact point.
In one advantageous embodiment of the invention, the lower contact surface of the cutting insert is designed as an arc with the radius (R), while the lower contact surface of the recess is designed with the radius (r) only at the beginning and the end of the arc, while the intervening space is separated by a clearance from the arc.
In this manner, a particularly easy insertion and positioning of the cutting insert in the recess is achieved.
In another advantageous configuration of the invention, the upper contact surface of the cutting insert is designed as a straight line normal to the symmetry line (S) and the application of the clamping force occurs at a contact point (K) on the contact surface of the clamping arm, also designed as a straight line.
In this manner, a particularly good transfer of the clamping force to the rearward contact surfaces is realized.
It has been shown to be especially advantageous for the contact surfaces of the cutting insert and the recess to be of V-shaped configuration in cross section, whereby twisting and tilting of the cutting insert in the recess is reduced.